1. Field of the Invention
The present invention relates to water repellent gypsum compositions which have excellent characteristics not found in conventional gypsum compositions.
2. Description of the Prior Art
Gypsum products such as gypsum boards, lath boards, decorated boards, sound-insulation boards and the like, have various characteristics depending upon the nature of gypsum, but suffer from the disadvantage that they are deteriorated by absorbing water. Accordingly, the utilization of gypsum-type construction products has been limited, although gypsum-type construction products have remarkable advantages of high flame-resistance, high sound-insulation properties, and high strength and low cost.
Most gypsum products made of gypsum boards comprise a gypsum core and paper adhered on both surfaces of the core.
Heretofore, various experiments have been conducted in attempts to prepare water-resistant gypsum board. The following methods have been proposed:
1. A water-resistant material such as cloth or paper is used to coat one or both surfaces of the gypsum board.
2. A water repellent agent such as paraffins, metal soaps, diamides, etc., is used to coat one or both surfaces of the gypsum board.
3. A water impermeable film is used to coat the surfaces of the gypsum board.
4. The water repellent agent of (2) is admixed in the core.
In cases (1) and (2), the water resistance of the gypsum boards, attained by covering or coating with the water resistant material or the water repellent agent has been unsatisfactory and the processing operation has been quite difficult for industrial operations because of inferior adhesiveness. In case (3), sufficient water resistance can be imparted for the gypsum board.
However, when the gypsum board is used after being cut, the desired water resistance cannot be imparted on the cut surface. Therefore, it is necessary to use some sort of decoration on the surface of the gypsum board, thereby causing high cost.
In case (4), it is also possible to improve water resistance, but the adhesiveness between the paper and the core is not sufficient. Thus it is difficult to use in practice.
These conventional water resistant materials and water repellent agents have been relatively difficult to be used effectively.
In general, the conventional water resistant gypsum boards are inferior to the usual gypsum boards with respect to their physical properties, especially the strength of the boards and the adhesiveness between core and paper. When gypsum boards absorb water, the physical properties are remarkably decreased.
Accordingly, there is a need for gypsum boards which have high water resistance so that they can be used as interior material or outdoor material at locations in which they will be drenched, such as bases of roofs and other water contacting places which are easily prepared and easily processed and which have the above-mentioned physical properties.